1. Field of Invention
This invention relates to timepieces with alarms and more particularly to means for setting the alarm time in a timepiece.
2. Prior Art
Electronic timepieces such as tuning leaf timepieces, tuning fork timepieces, quartz crystal timepieces, etc., offer greater precision than conventional mechanical timepieces. In cases where acoustic alarm devices have been installed in these timepieces, however, they have suffered from a major drawback. The drawback is that the improved precision of the timepiece has not effectively contributed to the acoustic alarm action due to the fact that the accuracy with which the time at which the alarm sounds can be set is poor. Normally, in conventional alarm setting devices, the acoustic alarm signal is produced by a cam mechanism installed between an hour hand wheel which revolves at an extremely low rate of one revolution in 12 or 24 hours and a corresponding alarm setting wheel. In such a conventional device, the accuracy with which the time at which the alarm sounds can be set is determined by the degree of precision of the parts of the cam mechanism, the excentricity or bearing clearance of the hour hand wheel and the alarm setting wheel, etc. Accordingly, in the case of a cam mechanism installed on the slowly revolving hour hand wheel, variations in the degree of mechanical precision have a great effect upon the degree of accuracy with which time at which the alarm sounds can be set. Therefore, since there are limits to the extent to which the degree of precision of the various parts can be improved, a reduction in the degree of accuracy with which the time at which the alarm sounds can be set is unavoidable.
A device which contains a primary cam mechanism which acts in conjunction with the hour hand wheel and a secondary cam mechanism which acts in conjunction with a wheel which revolves at a higher rate than the hour hand wheel, in which the degree of accuracy with which the time at which the alarm sounds can be set has been improved by combining separate contacts whose on-off conditions are controlled by two cam mechanisms, has been proposed in the past as an improved alarm setting device.
However, this improved device suffers from several drawbacks. First, simplicity of assembly suffers due to the increase in the number of parts and the probability of electrical contact malfunction is increased. Secondly, the load of the cam mechanism on the wheel turning at a higher rate causes the timepiece to lose driving torque and therefore exerts a deleterious effect upon the precision of the timepiece. This last effect is understandable in view of the fact that despite its small rotational torque, the wheel revolving at a higher rate requires at least a certain amount of operating force in order to obtain sufficient contact pressure to insure good contact.
This invention has been designed with the above mentioned conventional problems in mind.
cl SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide an alarm setting device which allows the time at which the alarm sounds to be set with a high degree of accuracy.
It is still another purpose of the present invention to provide an alarm setting device which is easy to assemble.
It is still another object of the present invention to provide an alarm setting device which is easy to operate.
In keeping with the principals of the present invention, the objects are accomplished with a unique alarm setting device for timepieces including a primary alarm setting wheel which engages an alarm hand wheel, a primary time wheel which is provided on the same shaft as the primary alarm setting wheel and which is driven by a wheel train of the timepiece, a primary cam mechanism which includes projections and engaging slots provided on the primary time wheel and in the primary alarm setting wheel, a secondary alarm setting wheel which engages with the primary alarm setting wheel, a secondary time wheel which is mounted on the same shaft as the secondary alarm setting wheel and which is driven at a higher rate than that of the primary time wheel by a wheel train of the timepiece, a secondary cam mechanism which includes projections and engaging slots provided on the secondary time wheel and in the secondary alarm setting wheel and whose dropping in and riding-up actions follow those of the primary cam mechanism and a contact means which includes a movable part which is engaged by the primary and secondary wheels and activated by the primary and secondary cam mechanisms and which controls the on-off condition of the contact means. dr